rainpl

Syntax

Description

L = rainpl(range,freq,rainrate) returns
the signal attenuation, L, due to rainfall. In
this syntax, attenuation is a function of signal path length, range,
signal frequency, freq, and rain rate, rainrate.
The path elevation angle and polarization tilt angles are assumed
to zero.

The rainpl function applies the International
Telecommunication Union (ITU) rainfall attenuation model to calculate
path loss of signals propagating in a region of rainfall [1]. The function applies when the signal
path is contained entirely in a uniform rainfall environment. Rain
rate does not vary along the signal path. The attenuation model applies
only for frequencies at 1–1000 GHz.

Signal Attenuation Due to Rainfall as Function of Polarization

Compute the signal attenuation due to heavy rainfall as a function of the polarization tilt angle. Assume a path distance of 100 km, a signal frequency of 100 GHz signal, and a path elevation angle of 0 degrees. Set the rainfall rate to 10 mm/hour. Plot the signal attenuation versus polarization tilt angle.

Signal path elevation angle, specified as a real-valued scalar,
or as an M-by-1 or 1-by- M vector.
Units are in degrees between –90° and 90°. If elev is
a scalar, all propagation paths have the same elevation angle. If elev is
a vector, its length must match the dimension of range and
each element in elev corresponds to a propagation
range in range.

Tilt angle of the signal polarization ellipse, specified as
a real-valued scalar, or as an M-by-1 or 1-by- M vector.
Units are in degrees between –90° and 90°. If tau is
a scalar, all signals have the same tilt angle. If tau is
a vector, its length must match the dimension of range.
In that case, each element in tau corresponds
to a propagation path in range.

The tilt angle is defined as the angle between the semimajor
axis of the polarization ellipse and the x-axis.
Because the ellipse is symmetrical, a tilt angle of 100° corresponds
to the same polarization state as a tilt angle of -80°. Thus,
the tilt angle need only be specified between ±90°.

Example: [45,30]

Output Arguments

L — Signal attenuationreal-valued M-by-N matrix

Signal attenuation, returned as a real-valued M-by-N matrix.
Each matrix row represents a different path where M is
the number of paths. Each column represents a different frequency
where N is the number of frequencies. Units are
in dB.

More About

Rainfall Attenuation Model

This model calculates the attenuation of signals
that propagate through regions of rainfall.

Electromagnetic signals are attenuate when propagating through
a region of rainfall. Rainfall attenuation is computed according to
the ITU rainfall model Recommendation ITU-R P.838-3: Specific
attenuation model for rain for use in prediction methods.
The model computes the specific attenuation (attenuation per kilometer)
of a signal as a function of rainfall rate, signal frequency, polarization,
and path elevation angle. To compute the attenuation, this model uses

γr=krα,

where r is
the rain rate in mm/hr. The parameter k and exponent α depend
on the frequency, the polarization state, and the elevation angle
of the signal path. The specific attenuation model is valid for frequencies
from 1–1000 GHz.

To compute the total attenuation for narrowband signals along
a path, the function multiplies the specific attenuation by a propagation
distance, R. Then, total attenuation is Lr =
Rγr. Instead of using geometric
range as the propagation distance, the toolbox uses a modified range.
The modified range is the geometric range multiplied by a range factor

11+RR0

where

R0=35e−0.015r

is the effective path
length in kilometers (see Seybold, J. Introduction to RF
Propagation.) When there is no rain, the effective path
length is 35 km. When the rain rate is, for example, 10 mm/hr, the
effective path length is 30.1 km. At short range, the propagation
distance is approximately the geometric range. For longer ranges,
the propagation distance asymptotically approaches the effective path
length.

You can apply the attenuation model to wideband signals. First,
divide the wideband signal into frequency subbands and apply attenuation
to each subband. Then, sum all attenuated subband signals into the
total attenuated signal.